Process using alumina agglomerates to eliminate organic oxygen-containing molecules present in an organic effluent

ABSTRACT

A process for eliminating organic oxygen-containing molecules such as alcohols and organic present in an organic or gaseous effluent is characterized in that the elimination is carried out by adsorbing said organic oxygen-containing molecules onto alumina agglomerates.

The invention relates to the field of eliminating impurities containedin organic industrial effluents in the liquid or gas state. Moreprecisely, it relates to eliminating oxygen-containing impurities byadsorption onto alumina agglomerates.

Many gaseous or liquid industrial effluents contain impurities whichshould be eliminated. However, such impurities can cause environmentalproblems, for example. More broadly, keeping the impurities in theeffluent can cause problems as regards quality (coloring the effluent,for example) or can have a negative influence on downstreamtransformation (destroying a catalyst required for a chemical reaction,or side reactions resulting in a drop in selectivity). Impuritiesencountered in industry that should be eliminated include alcohols andorganic acids and, in general, organic oxygen-containing molecules.

Impurities can be eliminated from a liquid industrial effluent bydistillation. The costs of such an operation are often high, andfurther, such a method cannot overcome all of the technical problemsthat arise, for example degradation of the essential components of theeffluent which can be caused by a rise in temperature. Further, theimpurities are often present in only trace amounts (less than 1%),rendering the use of distillation disproportionate. Finally, thedistillation temperatures of the different constituents of the effluentand of the impurities are not always sufficiently different to enablesuch a method to be used.

In certain specific cases, the impurities can be eliminated by washingwith a suitable solvent. That solution, however, is not always suitableand in any case, treating the used solvent is a problem that is becomingincreasingly difficult.

Consequently, using a solid adsorbent can often constitute a pertinentsolution to the problem. That technical solution can be used with aneffluent to be purified which is in a liquid or gas form.

To this end, it is known to use alumina agglomerates as a solidadsorbent, in particular to eliminate impurities constituted byoxygen-containing organic compounds such as alcohols and organic acidspresent in an organic effluent.

The aim of the invention is to provide users with a process exhibitingoptimum performance to eliminate the oxygen-containing organicimpurities comprised in an organic effluent.

To this end, the invention provides a process for eliminating organicoxygen-containing molecules, such as alcohols or organic acids, presentin an organic or gaseous effluent, the process being characterized inthat said elimination is carried out by adsorbing said organicoxygen-containing molecules onto alumina agglomerates with the followingcharacteristics:

-   -   a specific surface area of 10 square meters per gram (m²/g) or        more, preferably 30 m²/g or more;    -   optionally containing one or more doping compounds selected from        alkali metal compounds, alkaline-earth metal compounds and rare        earth compounds with a total content by weight of said elements        of 50% or less, preferably 25% or less, more preferably in the        range 5000 parts per million (ppm) to 20%, still more preferably        in the range 5000 ppm to 12%;    -   if their doping compound content is 5000 ppm or more, their        total pore volume is 30 milliliters per hundred grams (ml/100 g)        or more, more preferably 35 ml/100 g or more, and their V₇₀ Å is        10 ml/100 g or more, preferably 15 ml/100 g or more, still more        preferably 22 ml/100 g or more, yet more preferably 28 ml/100 g        or more, and optimally 35 ml/100 g or more;    -   if their doping compound content is below 5000 ppm, their total        pore volume is 45 ml/100 g or more, preferably 50 ml/100 g or        more, more preferably 55 ml/100 g or more, and their V₇₀ Å is 15        ml/100 g or more, preferably 22 ml/100 or more, more preferably        28 ml/100 g, and optimally 35 ml/100 g or more.

Said doping compounds are preferably selected from compounds based onsodium, potassium, calcium, magnesium, and lanthanum.

Said alumina agglomerates may comprise a sodium compound as the solecompound.

Said alumina agglomerates may be in the form of beads.

The diameter of said beads may be in the range 0.5 millimeters (mm) to10 mm, preferably in the range 0.7 mm to 8 mm, more preferably in therange 0.8 mm to 5 mm.

The alumina agglomerates may also be in the form of extruded materials.

They may be in the range 0.5 mm to 5 mm in size, preferably in the range0.7 mm to 3 mm.

Said organic effluent may be a hydrocarbon or a mixture of hydrocarbons.

Said elimination may be carried out at ambient temperature.

The alumina agglomerates are regenerated, preferably periodically, bytreatment in a stream of hot gas.

Said hot gas may be an inert gas the temperature of which may be atleast 130° C., preferably at least 200° C., more preferably at least230° C.

Said hot gas may be an oxidizing gas mixture or gas the temperature ofwhich is at least 150° C. preferably at least 200° C.

Said oxidizing gas mixture or gas is preferably selected from air,another oxygen/nitrogen mixture and a mixture containing steam.

To regenerate the alumina agglomerates, it is possible to employ aplurality of hot gases in succession, each of said hot gases being oneof the types cited above.

As will be seen, the invention consists of endowing alumina agglomeratesused during an operation for adsorbing oxygen-containing organiccompounds from an organic effluent with a particular morphology in thecombined terms of specific surface area, total pore volume and volumerepresented by pores with a diameter of 70 Angstroms (Å) or more. Theinventors have established that such agglomerates are remarkablysuitable for adsorbing oxygen-containing organic compounds.

The efficacy of aluminas for the envisaged application can be furtherstrengthened if “doping” products constituted by compounds based onalkali metals or alkaline-earth metals or rare earths are added. Thesedopants render it possible to obtain the desired results with lowerporosities for these aluminas.

The total pore volume (TPV) and the volume represented by pores with adiameter of 70 Å or more (V₇₀ Å) can be measured for an alumina sampleusing a conventional mercury porisimetric method.

To this end, the alumina sample is placed in a column into which mercuryis introduced at a pressure P. Mercury does not wet alumina, and so itspenetration or otherwise into pores with a given diameter in a sample isa function of the value of P. Finer pores require a higher pressure tofill them than coarser pores. Measuring the quantity of mercurypenetrating into the sample at different values of P allows the volumeoccupied by pores with a diameter that is higher than the values givenfor that diameter to be determined. Applying the highest possiblepressure P produces the TPV.

The alumina can be in any conventional form: powder, beads, extrudedmaterials, crushed material, or monoliths. Beads and extrudates arepreferred. The size of the beads will then usefully be in the range 0.5mm to 10 mm, preferably between 0.7 mm and 8 mm, and more preferablybetween 0.8 mm and 5 mm. The extrudates can be cylindrical or polylobedin shape, and solid or hollow; they are usefully in the range 0.5 mm to5 mm in size, preferably in the range 0.7 mm to 3 mm.

Alumina agglomerates with a standard composition can be employed for theenvisaged use, prepared and formed using any known method for producingthe desired porosity characteristics. By way of example, the beads canbe obtained using a rotary apparatus, by agglomerating an alumina powderin a bowl granulator or a drum. As is well known, that type of methodproduces beads with a controlled diameter and pore distribution, saiddimensions and distributions generally being produced during theagglomeration step. The porosity can be produced by different means,such as the choice of the granulometry of the alumina powder oragglomerating a plurality of alumina powders with differentgranulometries. A further method consists of mixing a compound known asa pore-forming agent with the alumina powder before or during theagglomeration step, which pore-forming agent disappears on heating andthus creates the porosity in the beads. Examples of pore-forming agentsthat can be cited are wood flour, wood charcoal, sulfur, tars, plasticsmaterials or emulsions of plastics materials such as polyvinyl chloride,polyvinyl alcohols, naphthalene, or the like. The quantity ofpore-forming agents added is determined by the desired volume. One ormore heat treatments can then finish bead formation. The extrudates canbe obtained by mixing and then extruding an alumina gel or an aluminapowder or a mixture of different starting materials.

The initial alumina powder can be obtained by rapidly dehydrating analuminum hydroxide or oxyhydroxide (for example hydrargillite).

The porosity characteristics demanded by the invention when the aluminaagglomerates have a standard composition are as follows:

-   -   a specific surface area of 10 m²/g or more, preferably 30 m²/g        or more;    -   a TPV of 45 ml/100 g or more, preferably 50 ml/100 g or more,        more preferably 55 ml/100 g or more;    -   a V₇₀ Å of more than 15 ml/100 g, preferably 22 ml/100 g or        more, more preferably 28 ml/100 g or more, optimally 35 ml/100 g        or more.

However, the best results are obtained when instead of aluminaagglomerates with a standard composition, alumina agglomerates are usedinto which one or more “doping” components constituted by alkali metalcompounds, alkaline-earth metal compounds or rare earth compounds havebeen incorporated. Preferably, compounds based on sodium, potassium,calcium, magnesium or lanthanum are selected. Sodium is a preferredexample, which can be introduced in the form of one or more precursorsof its oxide Na₂O.

Doping compounds can be added before or after the forming operation, orduring it.

The doping compounds are present in the alumina agglomerate as a totalmass content of less than 50%, preferably less than 25%, advantageouslyin the range 5000 ppm to 20%, and optimally in the range 5000 ppm to12%. Too high a doping compound content substantially reduces thealumina content and therefore the surface area of the adsorbent.

These doping compounds can accentuate the adsorbent properties of thesurface of the alumina agglomerates as regards the oxygen-containingorganic molecules to be eliminated. Their use in an amount of more than5000 ppm can, for the same result, reduce the requirements imposed onagglomerate porosity. The specific surface area required remains 10 m²/gor more, or even 30 m²/g or more, but the minimum TPV can be reduced to20 ml/100 g, preferably 30 ml/100 g, more preferably 35 ml/100 g. Theminimum V₇₀ Å can be reduced to 10 ml/100 g. Preferably, it is 15 ml/100g or more, more preferably 22 ml/100 g or more, still more preferably 28ml/100 g or more, and optimally 35 ml/100 g or more.

The invention has particular application to purifying a liquid orgaseous organic effluent constituted by a hydrocarbon or a mixture ofhydrocarbons, which may be saturated or unsaturated, aliphatic and/oraromatic, and wherein the amount of organic oxygen-containing compoundssuch as alcohols and organic acids is to be reduced. The operation isparticularly effective with a liquid effluent.

The alcohol or alcohols to be eliminated have general formula R—OH inwhich R contains at least one carbon atom (thus excluding water fromthis application). It may be a compound comprising multiple alcoholfunctions (in particular diols or triols) even if the monoalcohols are apreferred target for alcohol elimination. The invention also encompassesphenolic compounds.

The organic acid or acids to be eliminated have general formula R—COOH,R being a hydrogen atom or a radical containing at least one carbonatom. Such compounds can comprise more than one acid function (dibasicor tribasic acids, for example).

The adsorption operation can usually be carried out at ambienttemperature or at a temperature close to ambient temperature, forexample in the range 0° C. to 60° C., but this condition is in no wayobligatory in the general case.

It is advisable to carry out a periodic regeneration of the aluminaemployed, to prolong its service life.

Such a regeneration treatment can be carried out by passing a stream ofa hot inert gas over the agglomerate (nitrogen or argon, for example) atabout 130° C., for example, if the impurities eliminated are essentiallyaliphatic alcohols. A temperature of less than 130° C. is acceptable ifthe treatment can be prolonged as a result.

When the impurities are essentially aromatic alcohols and/or organicacids, it is preferable to heat the gas stream to 200° C. or more, oreven to at least 230° C.

It is also possible to use a gas or a mixture of an oxidizing gas (suchas air, a different nitrogen/oxygen mixture, or a mixture containingsteam) heated to at least 150° C., or even to at least 200° C.

These treatments can be used in combination.

Examples of alumina agglomerates in accordance with the invention and ofcomparative examples are given below, as well as the results ofexperiments demonstrating the adsorbent capacities of these variousalumina agglomerates towards alcohols and organic acids mixed with ahydrocarbon.

The compositions and morphologies of the agglomerates used are shown inTable 1.

TABLE 1 Composition and morphology of alumina agglomerates used inexperiments references Invention alumina 1 2 3 4 5 6 7 form beads beadsbeads beads extrudates beads beads diameter (mm) 1.4–2.8 2–4 1.4–2.82.4–4 1.2 1.4–2.8 2.4–4 surface area (m²/g) 328 8 252 192 255 139 181TPV (ml/100 g) 43 52 40 71 56 114 65 V_(70Å) (ml/100 g) 15 52 14 62 43113 56 Na₂O (ppm) 3400 600 20000 600 600 500 10500

Agglomerates 1 and 2 are comparative examples that are not relevant tothe invention. Agglomerate 1 has an Na₂O content of less than 5000 ppmwhich was obtained naturally during its preparation. It has a largespecific surface area but a TPV that is slightly lower than the requiredlower limit, and a V₇₀ Å that is just on the minimum limit required.Agglomerate 2 has a low specific surface area that is below the requiredminimum, but a relatively high TPV and V₇₀ Å. Its Na₂O content wasreduced during treatments that were carried out during its manufacture.

Agglomerates 3, 4 and 5 are in accordance with the invention. They allhave a high specific surface area (somewhat lower than that forreference agglomerate 1).

Agglomerates 4 and 5 have a high TPV and V₇₀ Å; the Na₂O content ofagglomerate 4 was reduced in an identical manner to that for referenceagglomerate 2. The Na₂O content of agglomerate 5 is due to that of thestarting material used, which corresponds to a boehmite gel.

Agglomerate 3 has a low TPV and V₇₀ Å (even lower than those forreference agglomerate 1) but its Na₂O content was deliberately increasedto 2%. To this end, dry impregnation was carried out using a dilutesodium hydroxide solution on previously produced beads. After drying at100° C. for 2 hours, calcining was carried out for 2 hours at 400° C.

Adsorption of the following compounds mixed with cyclohexane by theseagglomerates was studied:

-   -   alcohols: tertioamyl alcohol, methanol, pentanol, phenol,        4-tertiobutylphenol, 2-tertiobutylphenol, carvacrol and        1,2-propanediol;    -   organic acids: acetic acid, n-benzoic acid, 2,2-dimethylbutanoic        acid, benzoic acid.

The tests were carried out as follows: a mixture constituted by 250 mlof cyclohexane and 1000 ppm or an alcohol or 500 volumes per million(vpm) of an organic acid was placed in a beaker. A sample of 0.5 g ofalumina (for the alcohols and benzoic acid) or 0.2 g of alumina (for theother organic acids) pre-treated in nitrogen for 2 hours at 300° C. wasplaced in the beaker, in a boat isolating the beads or extrudates fromthe stirring bar for the mixutre. A glass stopper closed the beaker toprevent the moisture in the system from being altered. The adsorptionprogress was followed by injecting samples from the mixture into a gaschromatograph.

The adsorption results are summarized in Tables 2 to 6 below; they areexpressed as the gain in weight of the alumina, considered afterpre-treatment, due to adsorption of an alcohol or organic acid.

TABLE 2 Adsorption of alcohol after 2 hours of reaction alcohol aluminaweight gain (g/100 g) 1000 ppm tertioamyl 1 5.5 alcohol 2 0.6 3 12.6 510.7 6 14.1 1000 ppm 1-pentanol 1 1.8 5 3.1

TABLE 3 Adsorption of alcohol after 18 hours of reaction alcohol aluminaweight gain (g/100 g) 1000 ppm phenol 1 9.6 2 0.8 5 12.3 1000 ppm 4-tBuphenol 1 6.2 2 6.9 4 8.1 5 11.0 6 10.5 7 8.7 1000 ppm 2-tBu-phenol 1 5.95 7.0 1000 ppm carvacrol 1 4.2 5 10.3 1000 ppm 1,2-propanediol 2 0.5 48.6

TABLE 4 Adsorption of alcohol after 320 hours of reaction weight alcoholalumina gain (g/100 g) 1000 ppm tertioamyl 1 23.9 alcohol 2 1.6 4 29.8 533.5

TABLE 5 Adsorption of organic acid after 20 hours of reaction organicacid alumina weight gain (g/100 g) 500 vpm acetic acid 1 7.9 2 0.3 3 9.55 12.5 500 vpm n-hexanoic acid 1 1.9 2 0.2 3 2.5 4 3.2 5 5.3 500 vpm2,2- 1 2.7 dimethylbutanoic acid 2 0.3 3 3.6 4 7.3 5 10.5 6 10.1 7 7.9500 vpm benzoic acid 1 2.2 2 0.2 3 3.5 4 10.3 5 14.9 6 13.8 7 11.5

TABLE 6 Adsorption of acid after 44 hours of reaction organic acidalumina weight gain (g/100 g) 500 vpm 2,2- 1 3.3 dimethylbutanoic acid 20.4 3 5.1 4 9.5 5 13.7 500 vpm benzoic acid 1 3.7 2 0.3 3 5.9 4 12.0 516.9 6 15.5 7 13.1

An analysis of these tests shows that the condition regarding a highspecific surface area for the alumina agglomerate is indispensable, assample 2 offers only mediocre adsorption results in all cases despite ahigh TPV and V₇₀ Å.

When aluminas 4, 5 and 6 in accordance with the invention, purified inNa₂O, are compared with reference alumina 1 which retains its normalNa₂O content but has a low TPV and V₇₀ Å, the aluminas of the inventionare systematically more advantageous.

Regarding alumina 3, which has a less advantageous TPV and V₇₀ Å thanreference alumina 1, but which has been doped with Na₂O, it proves to beconsistently superior to alumina 1 and when adsorbing tertioamylalcohol, it is even superior to alumina 5. Alumina 7, doped with Na₂Oand with a TPV and V₇₀ Å within the preferred ranges, performs evenbetter.

1. A process for eliminating organic oxygen-containing molecules presentin an organic or gaseous effluent, comprising: the steps of adsorbingsaid organic oxygen-containing molecules onto alumina agglomerates withthe following characteristics: a specific surface area of 10 m²/g ormore; a compound selected from the group consisting of alkali metalcompounds, alkaline-earth metal compounds and rare earth compounds witha total content by weight of said compounds of 50% or less; having atotal pore volume of 30 ml/100 g or more if a doping compound is 5000ppm or more, and their V₇₀ Å is 10 ml/100 g or more, or having a totalpore volume of 45 ml/100 g or more if the doping compound is below 5000ppm.
 2. A process according to claim 1, wherein said doping compound isselected from the group consisting of compounds based on sodium,potassium, calcium, magnesium and lanthanum.
 3. A process according toclaim 2, wherein said alumina agglomerates comprise a sodium compound.4. A process according to claim 1, wherein said alumina agglomerates arein the form of beads.
 5. A process according to claim 4, wherein thediameter of said beads is in the range 0.5 to 10 mm.
 6. A processaccording to claim 1, wherein the alumina agglomerates are in the formof extruded materials.
 7. A process according to claim 6, wherein thesize of said extruded materials is in the range 0.5 mm to 5 mm.
 8. Aprocess according to claim 1, wherein said organic effluent is ahydrocarbon or a mixture of hydrocarbons.
 9. A process according toclaim 1, wherein said eliminating is carried out at ambient temperature.10. A process according to claim 1, wherein the alumina agglomerates areperiodically regenerated by treatment in a stream of hot gas.
 11. Aprocess according to claim 10, wherein said hot gas is an inert gas. 12.A process according to claim 11, wherein the temperature of said inertgas is at least 130° C.
 13. A process according to claim 10, whereinsaid hot gas is an oxidizing gas mixture or gas the temperature of whichis at least 150° C.
 14. A process according to claim 13, wherein saidoxidizing gas mixture or gas is selected from air, a furtheroxygen/nitrogen mixture and a mixture containing steam.
 15. A processaccording to claim 10, wherein a plurality of hot gases are used insuccession to regenerate the alumina agglomerates, said hot gases beinginert.
 16. The process of claim 1 wherein said compound is selected fromthe group consisting of alkali metal compounds, alkaline-earth metalcompounds and rare earth compounds with a total content by weight ofsaid compounds of 5000 ppm to 12%.
 17. The process of claim 1, whereinsaid doping compounds, alkaline-earth metal compounds and rare earthcompounds when their doping compound content is 35 ml/100 ppm or more,and the total pore volume is 35 ml/100 g or more, and their V₇₀ Å is 35ml/100 g.